Grimgrin, Corpse-Born, and Elemental Mastery

Prerequisites

• Grimgrin, Corpse-Born on the battlefield
• Elemental Mastery on the battlefield

Steps

1. Activate Grimgrin by tapping it, creating a number of Elemental tokens with haste equal to Grimgrin's power
2. Activate Grimgrin by sacrificing an Elemental token to untap Grimgrin and to put a +1/+1 counter on Grimgrin
3. Repeat

Results

• Infinite +1/+1 counters on Grimgrin
• Infinite creature tokens with haste
• Infinite ETB